Those skilled in the art of drilling applications for oil and gas will appreciate that a great deal of time can be consumed by various operations during the course of drilling a well. Among other things, each time a drill string needs to be tripped out of a wellbore, a potentially substantial amount of time is lost to drilling operations. Because the daily cost of drilling a well can be substantial, especially in connection with offshore drilling in deepwater applications, efforts have been made to reduce the time spent on tripping operations. Similarly, efforts have been made to try to speed up and obtain greater efficiencies in drilling operations generally. Specifically, efforts have been made to try to maintain the continuous and near continuous drilling of the well. The inputs that the driller has at his disposal to manage the well are rotation of the drill pipe, hoisting (raising or sometimes lowering) the drill pipe, and the circulation of fluid down through the drill pipe and back to the surface. A significant problem with existing drilling techniques is that they require the drill pipe to stop at the drillfloor to be connected to the next section of drill pipe entering or being pulled from the well. During this stopping period all dynamic inputs used by the driller to manage the well stops because the drilling equipment can no longer rotate, hoist or pump fluids while moving. It is during this stopping time, or connection time, that the well experiences many of the classic well management issues that cause non-productive time (NPT). Of course, such efforts must be taken with care so as not to compromise safety and to also prevent or minimize the potential for accidents or pollution.
One approach taken in the past involves the use of a “multi-activity” drilling assembly which includes two tubular stations. Such an approach is described in U.S. Pat. No. 6,085,851, issued to Scott, et al., on Jul. 11, 2000, titled “Multi-Activity Offshore Exploration and/or Development Drill Method and Apparatus (“Scott”),” which is hereby incorporated by reference as if fully set forth herein. In Scott, an apparatus and method is described that involves the use of two drill strings so that certain auxiliary actions can be ongoing with respect to one drill string while drilling or tripping operations are ongoing with respect to a second drill string. This approach has certain drawbacks, not least of which are the use of two drill strings and the added complexity of ongoing operations with both in connection with a single derrick.
What is needed is an apparatus and methods for drilling and tripping that take less time than standard drilling and tripping equipment and methods.